The present invention relates generally to radio frequency identification (RFID) antennas and tags, and methods of manufacturing RFID antennas and tags. More specifically, the present invention is directed toward vacuum metallized antennas for RFID tags and enclosures for protecting an integrated circuit of the RFID tag.
RFID tags are currently used to track and monitor inventory locations and communicate information and data about the product, substance, or person, they are attached to such as part number, descriptions, lot codes and other pertinent product information similar to information currently contained within a standard universal product (UPC) bar code. However, UPC bar code technology is an optical technology and is limited to line of site orientation. This limitation requires that the bar code reader which scans the bar code must be able to visually see the bar code label applied to the product in order to scan and read/record information. The advantage RFID tags have over bar code is that RFID technology is radio frequency based and does not require any visual line of site between the product ID tag and the reader or scanner. This allows the RFID tag and the reader to exchange information freely, regardless of the orientation of the ID tag, as long as the tag is within the readers scanning range. RFID tags can be read through packaging, containers, or through other products. In addition, RFID readers can read and identify any RFID tag that is within its scanning range all at once, without having to scan each individual item as is currently required with UPC bar codes. For example, while shopping in a grocery store, if all items were to have individual RFID tags, theoretically, the shopper would be able to simply walk through a scanner in a check out line and all items in their cart would be scanned and the customer charged accordingly without having to remove a single item from their cart. Other advantages for RFID tags would be for use with inventory management, automatic reordering when inventory levels fall below a set level, or security alerts for when items are removed from a particular location without authorization.
RFID is based upon using radio frequency (RF) signals to communicate information between small (generally less 25 mm to 300 mm on the largest side) RF receiver/transmitter devices and other electronic equipment used for “reading” the information contained in the memory circuitry of the small electronic device (the RFID tag). RFID tags are used to track and monitor the location of objects located in inventory and communicate information such as part number, descriptions, lot codes and other pertinent product information similar to information currently contained within a standard universal product (UPC) bar code. Additional electronic equipment (a.k.a., “reader”) is used to both detect and collect information from the RFID tag. Typically, the reader will poll the RFID tag by sending an RF signal containing short instructions that ask the RFID tag to respond. The RFID tag, using either its own energy or the energy contained in the polling RF signal, to respond to the reader with the requested information. In current practice, an RFID device is placed onto a carrier medium, which is subsequently adhered to the object to be tracked.
While the possibilities for using RFID tags are ever increasing, the manufacturing costs for generating these RFID tags has to be addressed. The cost for manufacturing the tags has currently limited the use of RFID tags to pallets of products or to high dollar items such as compact discs, DVD's, or to high theft items such as Gillette razor blades where the cost of the tags are justifiable. This particular invention pertains to various methods and devices for manufacturing low cost RFID tags suitable for use on inexpensive everyday items.
RFID tags generally include a small passive integrated circuit chip attached to a thin polymer substrate that has been screened (similar to silk-screening) with a metal layer, the metal layer comprising an antenna sub-assembly. The RFID tag may be completed with an overlay of thin polymer film (or in some cases nothing is provided) as a means of providing minimal protection from the environment. As can be appreciated, the RFID tag is subject to mechanical abuse and or tampering and is exposed to environmental conditions that may impede the longer term performance of the RFID tag.
An important aspect of the antenna sub-assembly is the quality of the metal conductive layer in terms of electrical performance, as measured by antenna gain. Presently, a number of different methods may be used to accomplish a metalized shape on a substrate. For instance, a copper cladded foil can be etched to reveal an antenna shape. This process requires that a film material be first metalized completely, a mask applied (in the form of a deposition of another material in a prescribed shape, and subsequent etching to remove unwanted material. This process has the obvious cost disadvantages; however, the resulting metal layer (typically several micrometers of copper) provides adequate performance and reasonable adhesion to the film, albeit at a relatively high cost.
Film materials can be metalized using both conductive ink and conductive paint; however, the disadvantages of conductive paint (tendency to crack, environmental issues, need for relatively high conductive particle loading to achieve low resistance, etc.) dictate against its use for RFID tag sub-assemblies. Conductive ink can readily be applied to film materials to provide the required conductivity and performance. While the conductive particles are still suspended in a carrier matrix, the overall performance is adequate and the primary cost driver is the conductive ink. Conductive ink layers are on the order of tens of micrometers thick, though thinner depositions may be possible.
While the conventional methods of manufacturing RFID tags have proven adequate, as the need for these tags increases, there are concerns that the metal screening process will be limited in its cost reduction potential. The current estimated need for RFID tags is in the billions of tags per year and growing to perhaps trillions of tags per year with continued cost reductions. Consequently, what are needed are methods and RFID tags that may be manufactured cheaply and when necessary provide for a robust construction sufficient to be withstand the environment.